Hopkins singles out spring for description and praise, since he feels that it is the time of year that brings mankind closest to the harmony of man and nature (and God) that existed in the biblical Garden of Eden. We get the feeling that praising nature in its various earthly aspects is, for our speaker, also a way of praising God, the creator. Without nature, it seems, he could not get so close to God.
By not referring to an "I" in the poem, Hopkins steers the poem away from being about a single, personal experience, and makes it about a broader relationship between mankind and nature.